Voltage measuring arrangement



May 10, 1932. T. LAURENT VOLTAGE MEASURING ARRANGEMENT Filed -.J an l4,v 1931 faimvewk Patented May 10, 193

UNITED ATENTfoFF ICE 'roRBEmv LAURENT, or srrooKHoLM, swnnnm nssie von To IITELEFQNAKTIEBOLAGET n. m. nnrcsson, or s'rooxnonm, SWEDEN, A COMPANY or svvrumn v e I "VOLTAGE MEASURING AR ANGEMENT Application filed January 14, m a No. 5os, 75o,{a'na"in Sweden January14, 1930.. I

The present invention'relates to arrangements for comparative measurement of small alternating voltages.

I v More particularly the invention relates to arrangements for transmission level measurements in telephone lines.

In telephone lines necessary to be able sion level in having repeaters it is to check the transmisdifferent points in order. to be able to determine the amplificationratio re quired at measurement of the telephone line has hitherto sending out a current (so called zero leveljand quency the various repeater stations. The, transmiss on level in a been effected by of, a certain voltage of a certain I fre from one end of the line and then measuring the resultant voltage in different points along the line by comparison (calibra tion) with a local current source of the same frequency as the current sent out. Consequently the sending station must at ,every measurement communicate informatlon with regard to. the frequency that has been sent, in

order that it shall be rious local oscillators i This system for measuring possible to adjust the va-, for the same frequency.

the transmission level is rather troublesome .and the results obtained arenot always accurate. The accuracy depends largely upon'whetherthe twovoltages to be compared have frequency andcurve exactly the same form which in the metho d hitherto usedis generally not the. case. rrors may arise especially thereby, that at one or both current sources different, diiferentreperiods are mutually the two half sults being then obtained depending on which half periods are compared. Corresponding errors of also met with in other measureme ilarkmd at which a voltmeter,

likewise connected alor the likerto be suba valve voltmeter; is ternatelyto the line measurement are ts of a sunpreferably j ected to measurement and'to a separate cur,- rent source over a calibrating dev1ce,' by way of example an adjustable a potentiometer. p

rtificial line or a by voltage from The above mentioned inconveniences are according to-the present invention eliminated thereby, that the separate current source consists of an electron valve amplifier controlled the object to be subjected to measurement. tions is the same in bothcases frequency and curve-form will be exactly alike; Hereby the measurement becomes .more accurate and no information is required from the terminal station with regard to the frequency to be used for themeasurements; which sometimes is a great advantage especially if the line runs-through several countries of different languages.

' 'As mentioned above the accuracy of the measurements depends largely upon whether the two voltages to be compared have the same curve form or not. One feature of the present invention is that'the voltmeter measures the same kind of half periods (either the positive or the negative) when connected to the object l to be subjected to measurement as when connected to the separate current source overthe calibrating device." This is of great importance as the positive and negative half periods may be of rather unequal form thus having a different influence on the measuring instruments. Another feature of the invention is that the voltage is tapped off from a resistance connected to'the object to be sub jected to measurement. For the purpose of preventing unsymmetrical currents from entering the measuring arrangement the resistmice is shunted with an inductance coil, the

middle point of whichis connected to the middle point of the resistance, the desired voltage being tapped off between said middle As the origin of the oscilla larly adapted for transmission level measurements, and Figure 2 shows another QIHbOCllment of the invention adapted to be used also for loop attenuation measurements and amplification measurements.

The measuringarrangement shown in Fig ure 1 comprisestwo potentiometers P P an amplifier F and a valve voltmeter V.

The potentiometerresistance P is in fseries with an equally greatresistance R connected into circuit between the two input terminals aa.

cuit in parallel .withsaid resistances. junction point between the two resistances P and R is by means of a grounded. junction line;- jlconnected to the middle point of the inductance coil D andfurther to one pole of the amplifierF, one pole of the potentiometer P and one poleof the-valve voltmeter V. "Theotherpole of the valve voltmeter V may by means of'a double throw switch 0 be alternately connected to the movable terminal of the potentiometer P or to the movable terminal of the potentiometer P and the other terminal of the amplifier F To the secondary side of the. amplifier circuit is connected including a thermo-couple ,T, to which a galvanometer G5 is connected, a variable resistance S, the potentiometer P and a resistance R connectedin series with the latter. The junction point between the potentiometer P and the resistance R is connected to the groundedwire .j. A galvanometer G is connectedto the valve voltmeter V.

The arrangement operates substantially in the following way. 1

The voltage Vxto be measured, for instance the transmission level in a telephone a line, is connected between the terminals a-a;

' The valve voltmeter V is by means of the double throw switch 0 connected to the potentiometer-P by means of which a certain voltage V,., corresponding to a certain deflectionv on the galvanometer G is tapped oil from the object to be subjected to measurement. This deflection may be adj usted' more accurately by means of a regulatingdevice on the valve voltmeter. By means of the variable resistance .S the deflection on the galva-nometer G is adjusted to a certain value corresponding to a voltage V over thegentirepotentiometer P The valve voltmeter V is now connectedover the double throw switch Oto said potentiometer. The movable terminal of the potentiometer P is thenv set in sucha way'that the deflection on the gal vanometer G1 obtains the same value as was obtained when the voltage was taken directly from the potentiometer P The voltage over 'Asthe An inductance coil D is connected into'ciry' 'detel'mlned' If one makes The ' mechanically connected measurement (by way of i the potentiometer P is then V,,=V The two potentiometers are graduated in neper and it is'as sumed, that at the measurement 6 neper has been read off the potentiometer P and (Z neper off the potentiometer P The voltage at said two potentiometers is thus:

V a' al -V,0: lived-k quantities it, Z) and d are known and h Vue"="0,77 5 Volts, (b+0Z) will be the transi mission. level expresseddirectly in neper.

in Figure 2 is shoi n a circuit diagramior an arrangement of'substantiallyt'he same construction as the one described inv connection with' Figure 1*," but which may also be used in resistance measurements and loop attenuation: measurements.

For" this purpose the transmission level meter is provided with an arrangement p ermitting the meter to be fed with alternating currentfroin a separate current source. Said "arrangement"comprises a potentiometer P 'a transformer Tm, two series-connected artifi cial lines or damping'networks KD' and KD of which the latter may be" disconnected by means of the switches O O and O and a doublethrow switch 0 for connecting said arrangement to the measuring arrangement;

Further a' galvanometer G common to'the twoarrangements is arrangedto beconnected alternatel'yto the the-rmo-couple T I I by means ofa'double throw switch 0 The double throw switch 0 is with another double throw" switch 0 which, when the galvanometer is switched over from the thermo couple T to the valve voltmeter V; simultaneously-connects a resistanceR into circuit instead of the heating wire of the thermocouple T. The resistance R isequal to the resistance or the thermo c'ouplje. In Figure 7 2 an outputt'ransformer T'r'gfor the amplifier F is also shown. When-measuring the loop attenuation the object M to be subjected to example a tele phone line or the like connected in a loop) is'con'nected between the terminals a a of the measuring arrangement and the terminals 6 of the dampingnetwork An alternating cur'rent'sourc'e' is 'colrnect'edto the terminals 0 0 of the potentiometer P The damping network KI)" is disconnectedby closing the switches 05, O and openingthe switch 0 .1 The fixed damping network KD is offsmall, dimensions and serves-only to damp "possible" {currents reflected 'fromthe object subjected to measurement. Inorder valve voltmeterV-orto the damping network double throw switch 0 has been switchedv over in its upper position the loop attenuation measurements are carrled out in the same manner as the transmlssion level'measurements described above in connection with Figure l. The valve voltmeter V is by means of the double throw switch 0 alternately connected to the potentiometer-s P and P the voltage transmitted directly from the transformer T73 being thus compared with the voltage transmitted indirectly over the object M subjected to measurement. The amplification ratio of an amplifier is measured in a similar manner except that the KD is connected into circuit (by opening the switches 0 7 and closing the switch 0 in order to convert the negative attenuation of the amplifier to a positive attenuation that can be measured.

The above described arrangements are only intended to illustrate how the invention may be carried into effect and said arrangements may therefore be varied in different ways without invention.

I claim 1 1. A device for voltage measurements comprising in combination an amplifier for alternating currents, means for connecting the amplifier to the voltage to be measured, an adjustable damping device connected with its input side to the output side of the amplifier, means for adjusting the alternating potential supplied to the input side of the damping device, and means for comparing the voltage to be measured with the voltage on the output side of the damping device.

2. A device for voltage measurements comprising in combination an amplifier for alternating currents, means for connecting the amplifier to the voltage to be measured, an adjustable damping input side to the output side of the amplifier, means for adjusting the alternating potential supplied to the input side of the damping device to a predetermined value, a voltmeter and means for applying the voltage to be measured and the output voltage of the adjustable damping device alternately to said voltmeter. Y

3. A device for voltage measurements comprising in combination an amplifier for alternating currents, means for connecting the amplifier to the voltage to be measured, an adjustable damping device connected with its input side to the output side of the amplifier, means for adjusting the alternating potential supplied to the input side of the damping device to a predetermined value, a voltmeter including a rectifier, and means for departing from-the idea of the I applying the voltage to be measured and the output voltage of the adjustable damping device alternately to said voltmeter in'such a manner as to rectifysemi-cyclesof the same sign in both cases.

4. A device for voltage measurements comprising in combination a potentiometer adapted to'be connected to the object to be subjected to measurement, an amplifier for alternating currents, means for connecting the amplifier to a pair of taps on the potentiometer, an adjustable damping device connected with its input side to the output side of the amplifier, means for adjusting the alternating potential supplied to the input side of the damping device, and means for comparing the voltage between said pair of taps with the voltage on the output side of the damping device.

e. A device for voltage measurements comprising subjected to measurement, an induction coil shunted across the potentiometer and having its middle point connected to a middle point of the, potentiometer, an amplifier for alternating currents, means for connecting the amplifierbctween said middle point and an adjustable tap of the potentiometer, an adjustable damping device connected with its input side to the output side of the amin combination a potentiometer adapted to be'connected to the object to be plifier,"means for adjusting the alternating potential supplied to the input side of the damping device, and means for comparing the voltage between said taps of the potentiometer with the voltage on the output side of the damping device. 4

In testimony whereof I affix my signature.

TORBERN LAURENT.

device connected with its 

